This invention relates to an apparatus for forming compacts from finely divided solid particles or a mixture of fine and coarse solid particles in a dry, semi-dry or plastic state. More specifically, this invention concerns a die for manufacturing relatively large compacts by applying ultra-high pressure to a mixture of such solid particles.
It is known in the art that if a sufficiently high pressure is applied to the mixtures of particles mentioned above, the particles will be compressed into a solid element. This solid element, referred to as a compact, is a highly densified, low-porosity agglomeration of particles. The ultra-high pressures required to form compacts usually exceed 100,000 psi, and may perhaps exceed 1,000,000 psi applied to the particles. The amount of pressure required will depend on the type of solid particles used, the sizes, gradations and strength of the particles, the amount of vibration applied to the particles, and the degree of density desired.
During formation of a compact, the initial volume taken up by the solids decreases and the density increases. That is, the discrete particles are brought closer together, some of the smaller particles fill in the spaces between the larger particles, some particles break into smaller particles, and some of the particles perhaps change shape, so that the spaces between the particles are substantially reduced. In this denser state, the individual particles tend to bind together by different phenomena, some of which are as yet unidentified. Some of these phenomena relate to friction at points of contact between the particles and some probably relate to bonds at the atomic level.
After compaction, some elastic energy remains in the particles, making the compact tend to expand outwardly after pressure is released. This residual elastic energy creates problems in removing the compact from the die in which it is formed. Unless the lateral forces retaining the compact are released simultaneously, the compact will tend to delaminate during removal from the die.
Specifically, existing dies are rigidly constructed. To remove the compact from such a die, one wall of the die is removed and the compact is extruded or ejected from the die. This results in a nonuniform release of pressure from the compact, causing delamination during extrusion or ejection. This is a problem in the formation of compacts by high pressure of any practical size suitable for use in industrial and commercial applications, i.e., for compacts larger than 1 cm. across.
Prior to the present invention, no die was capable of withstanding the ultra-high pressures necessary for forming compacts and at the same time providing a mechanism for removing the compact from the die without delamination. Using the present invention, compacts can be formed into any desired shape for industrial or commercial use. They can be formed into a wide variety of sizes and shapes for use in products such as roofing tiles, floor tiles, blocks, bricks, railroad ties, manhole covers, and architectural shapes. The present invention can also be used in powder metallurgy and ceramic products.
Compacts have significant advantages over traditional man-made products. They are considerably stronger, more durable, more volume stable, more dimensionally accurate, and less porous than conventional products. They can be formed of traditional construction materials, such as portland cement, blended cement, concrete, gypsum, fly ash, lime, natural cement, blast furnace cement, etc. For special applications, such as space shuttle tiles, materials such as cermets, graphite compacts, silica compacts, and metal powders could be used in the present invention.
Because of their increased strength, compacts can be made thinner and/or lighter in weight than conventional products, thereby reducing structural dead load. Additionally, the increased strength and dimensional accuracy of compacts result in a much lower rejection rate during manufacture, transportation and installation.